Analysing Antenna Ratio Dependence of Plasma Charging Damage with Weibull Breakdown Statistics
IMEC, Leuven, Belgium10/2000; DOI:10.1109/ESSDERC.2000.194831 ISBN: 2-86332-248-6 In proceeding of: Solid-State Device Research Conference, 2000. Proceeding of the 30th European
Source: IEEE Xplore
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ABSTRACT: The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological and meteorological conditions.Journal of Radioanalytical and Nuclear Chemistry 01/2007; 274(3):531-538. · 1.47 Impact Factor
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ABSTRACT: Beryllium-7 (7Be) and lead-210 (210Pb) activities were measured from October 2002 to January 2004 at Waliguan Observatory (WO: 36.287°N, 100.898°E, 3816 m a.s.l (above sea level) in northwest China. 7Be and 210Pb activities are high with overall averages of 14.7±3.5 mBq m−3 and 1.8±0.8 mBq m−3 respectively. For both 7Be and 210Pb, there are significant short-term and seasonal variations with a commonly low value in summer (May-September) and a monthly maximum in April (for 7Be) and in December (for 210Pb). The ratio of 7Be/210Pb showed a broad maximum extending from April to July, coinciding with a seasonal peak in surface ozone (O3). The seasonal cycles of 7Be and 210Pb activities were greatly influenced by precipitation and thermal dynamical conditions over the boundary layer, especially for 210Pb. The vertical mixing process between the boundary layer and the aloft air modulates the variations of 7Be and 210Pb at WO in summer. It is indicated that air mass had longer residence time and originated from higher altitudes at WO in the spring-summer time and the winter in 2003. During an event with extremely high weeklyaveraged 7Be concentration (24.8 mBq m−3) together with high O3 levels and low water mixing ratio, we found that air masses had been convectively transported a long distance to WO from high latitude source regions in central Asia, where significant subsiding motions were observed. In another case with the extreme 210Pb activity of 5.7 mBq m−3 high CO2 level and specific humidity (in winter), air masses had come from south China and north Indian regions where 222Rn activities were high. This study, using 7Be and 210Pb as atmospheric tracers, has revealed that complex interactions of convective mixing from the upper troposphere and long-range transports exist at WO.Advances in Atmospheric Sciences 01/2008; 25(3):404-416. · 1.34 Impact Factor
Article: Beryllium7 aerosols in ambient air[show abstract] [hide abstract]
ABSTRACT: The aerodynamic size distribution of 7Be in ambient aerosol particles was determined using l-ACFM cascade impactors. The activity distribution of 7Be measured by gamma spectrometry (Eγ = 477 keV) was largely associated with submicrometer aerosols in the accumulation mode (0.4 to 2.0 μm). The activity median aerodynamic diameter (AMAD) ranged from 0.76 to 1.18 μm (average 0.90 μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, σg, ranged from 1.86 to 2.77 (average 2.24). In 65% of the cascade impactor measurements, the activity distributions of 7Be showed maxima in the 0.7 to 1.1 μm size range. Low AMADs as low as 0.62 to 0.74 μm of 7Be aerosols have been observed at locations characterized with relatively low pollution. Some dependency of AMADs on height has been also observed. In marine environments, the 7Be activity size distribution was dominant in the upper size range of aerosol particles.Environment International - ENVIRON INT. 01/1996; 22:125-130.
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